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Date: Mon,  6 May 2024 21:54:32 -0700
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Subject: [PATCH v10 3/7] locking/mutex: Expose __mutex_owner()
From: John Stultz <jstultz@google.com>
To: LKML <linux-kernel@vger.kernel.org>
Cc: Juri Lelli <juri.lelli@redhat.com>, Joel Fernandes <joelaf@google.com>, 
	Qais Yousef <qyousef@layalina.io>, Ingo Molnar <mingo@redhat.com>, 
	Peter Zijlstra <peterz@infradead.org>, Vincent Guittot <vincent.guittot@linaro.org>, 
	Dietmar Eggemann <dietmar.eggemann@arm.com>, Valentin Schneider <vschneid@redhat.com>, 
	Steven Rostedt <rostedt@goodmis.org>, Ben Segall <bsegall@google.com>, 
	Zimuzo Ezeozue <zezeozue@google.com>, Youssef Esmat <youssefesmat@google.com>, 
	Mel Gorman <mgorman@suse.de>, Daniel Bristot de Oliveira <bristot@redhat.com>, Will Deacon <will@kernel.org>, 
	Waiman Long <longman@redhat.com>, Boqun Feng <boqun.feng@gmail.com>, 
	"Paul E. McKenney" <paulmck@kernel.org>, Metin Kaya <Metin.Kaya@arm.com>, 
	Xuewen Yan <xuewen.yan94@gmail.com>, K Prateek Nayak <kprateek.nayak@amd.com>, 
	Thomas Gleixner <tglx@linutronix.de>, kernel-team@android.com, 
	Metin Kaya <metin.kaya@arm.com>, Valentin Schneider <valentin.schneider@arm.com>, 
	"Connor O'Brien" <connoro@google.com>, John Stultz <jstultz@google.com>
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From: Juri Lelli <juri.lelli@redhat.com>

Implementing proxy execution requires that scheduler code be able to
identify the current owner of a mutex. Expose __mutex_owner() for
this purpose (alone!).

Cc: Joel Fernandes <joelaf@google.com>
Cc: Qais Yousef <qyousef@layalina.io>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: Valentin Schneider <vschneid@redhat.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Ben Segall <bsegall@google.com>
Cc: Zimuzo Ezeozue <zezeozue@google.com>
Cc: Youssef Esmat <youssefesmat@google.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Daniel Bristot de Oliveira <bristot@redhat.com>
Cc: Will Deacon <will@kernel.org>
Cc: Waiman Long <longman@redhat.com>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: "Paul E. McKenney" <paulmck@kernel.org>
Cc: Metin Kaya <Metin.Kaya@arm.com>
Cc: Xuewen Yan <xuewen.yan94@gmail.com>
Cc: K Prateek Nayak <kprateek.nayak@amd.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: kernel-team@android.com
Tested-by: K Prateek Nayak <kprateek.nayak@amd.com>
Tested-by: Metin Kaya <metin.kaya@arm.com>
Reviewed-by: Metin Kaya <metin.kaya@arm.com>
Reviewed-by: Valentin Schneider <vschneid@redhat.com>
Signed-off-by: Juri Lelli <juri.lelli@redhat.com>
[Removed the EXPORT_SYMBOL]
Signed-off-by: Valentin Schneider <valentin.schneider@arm.com>
Signed-off-by: Connor O'Brien <connoro@google.com>
[jstultz: Reworked per Peter's suggestions]
Signed-off-by: John Stultz <jstultz@google.com>
---
v4:
* Move __mutex_owner() to kernel/locking/mutex.h instead of
  adding a new globally available accessor function to keep
  the exposure of this low, along with keeping it an inline
  function, as suggested by PeterZ
v10:
* Handle null lock ptr, to simplify later code, as suggested
  by Metin Kaya
---
 kernel/locking/mutex.c | 25 -------------------------
 kernel/locking/mutex.h | 27 +++++++++++++++++++++++++++
 2 files changed, 27 insertions(+), 25 deletions(-)

diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c
index 6d843a0978a5..4b7193fd3be9 100644
--- a/kernel/locking/mutex.c
+++ b/kernel/locking/mutex.c
@@ -56,31 +56,6 @@ __mutex_init(struct mutex *lock, const char *name, struct lock_class_key *key)
 }
 EXPORT_SYMBOL(__mutex_init);
 
-/*
- * @owner: contains: 'struct task_struct *' to the current lock owner,
- * NULL means not owned. Since task_struct pointers are aligned at
- * at least L1_CACHE_BYTES, we have low bits to store extra state.
- *
- * Bit0 indicates a non-empty waiter list; unlock must issue a wakeup.
- * Bit1 indicates unlock needs to hand the lock to the top-waiter
- * Bit2 indicates handoff has been done and we're waiting for pickup.
- */
-#define MUTEX_FLAG_WAITERS	0x01
-#define MUTEX_FLAG_HANDOFF	0x02
-#define MUTEX_FLAG_PICKUP	0x04
-
-#define MUTEX_FLAGS		0x07
-
-/*
- * Internal helper function; C doesn't allow us to hide it :/
- *
- * DO NOT USE (outside of mutex code).
- */
-static inline struct task_struct *__mutex_owner(struct mutex *lock)
-{
-	return (struct task_struct *)(atomic_long_read(&lock->owner) & ~MUTEX_FLAGS);
-}
-
 static inline struct task_struct *__owner_task(unsigned long owner)
 {
 	return (struct task_struct *)(owner & ~MUTEX_FLAGS);
diff --git a/kernel/locking/mutex.h b/kernel/locking/mutex.h
index 0b2a79c4013b..cbff35b9b7ae 100644
--- a/kernel/locking/mutex.h
+++ b/kernel/locking/mutex.h
@@ -20,6 +20,33 @@ struct mutex_waiter {
 #endif
 };
 
+/*
+ * @owner: contains: 'struct task_struct *' to the current lock owner,
+ * NULL means not owned. Since task_struct pointers are aligned at
+ * at least L1_CACHE_BYTES, we have low bits to store extra state.
+ *
+ * Bit0 indicates a non-empty waiter list; unlock must issue a wakeup.
+ * Bit1 indicates unlock needs to hand the lock to the top-waiter
+ * Bit2 indicates handoff has been done and we're waiting for pickup.
+ */
+#define MUTEX_FLAG_WAITERS	0x01
+#define MUTEX_FLAG_HANDOFF	0x02
+#define MUTEX_FLAG_PICKUP	0x04
+
+#define MUTEX_FLAGS		0x07
+
+/*
+ * Internal helper function; C doesn't allow us to hide it :/
+ *
+ * DO NOT USE (outside of mutex & scheduler code).
+ */
+static inline struct task_struct *__mutex_owner(struct mutex *lock)
+{
+	if (!lock)
+		return NULL;
+	return (struct task_struct *)(atomic_long_read(&lock->owner) & ~MUTEX_FLAGS);
+}
+
 #ifdef CONFIG_DEBUG_MUTEXES
 extern void debug_mutex_lock_common(struct mutex *lock,
 				    struct mutex_waiter *waiter);
-- 
2.45.0.rc1.225.g2a3ae87e7f-goog